There's no formula. It's something to remember
Hex socket screw specifications Dimensions of the opposite side of the wrench
M32.5
M43
M54
M65
M86
M108
M1210
M1412
M1614
M2017
Internal plum cylindrical head screw wrench model
M2T6
M2.5T8
M3T10
M4T20
M5T25
M6T30
M8T45
M10T50
M12T55
M14T55
M16T60
M20T80
Feifan fastening system